On the massive star content of the nearby dwarf irregular Wolf-Rayet galaxy IC 4662

Abstract

Aims. We investigate the massive stellar content of the nearby dwarf irregular Wolf-Rayet galaxy IC 4662, and consider its global star forming properties in the context of other metal-poor galaxies, namely the SMC, IC 10 and NGC 1569. Methods. Very Large Telescope/FORS2 imaging and spectroscopy plus archival Hubble Space Telescope/ACS imaging datasets permit us to spatially identify the location, number and probable subtypes of Wolf-Rayet stars within this galaxy. We also investigate suggestions that a significant fraction of the ionizing photons of the two giant H ii regions A1 and A2 lie deeply embedded within these regions.Results. Wolf-Rayet stars are associated with a number of sources within IC 4662-A1 and A2, plus a third compact H ii region to the north west of A1 (A1-NW). Several sources appear to be isolated, single (or binary) luminous nitrogen sequence WR stars, while extended sources are clusters whose masses exceed the Orion Nebula Cluster by, at most, a factor of two. IC 4662 lacks optically visible young massive, compact clusters that are common in other nearby dwarf irregular galaxies. A comparison between radio and Hα-derived ionizing fluxes of A1 and A2 suggests that 30-50% of their total Lyman continuum fluxes lie deeply embedded within these regions. Conclusions. The star formation surface density of IC 4662 is insufficient for this galaxy to qualify as a starburst galaxy, based upon its photometric radius, R 25 . If instead, we were to adopt the V-band scale length R D from Hunter & Elmegreen, IC 4662 would comfortably qualify as a starburst galaxy, since its star formation intensity would exceed 0.1 M yr −1 kpc −2 .

The Wolf–Rayet Content of the Galaxies of the Local Group and Beyond

“…Other surveys have been carried out for WR stars in even more distant systems with the 8-m VLT by Lucy Hadfield, Joanne Bibby and Crowther: IC 4662 (2.3 Mpc) [106], NGC 7793 (3.4 Mpc) [107], NGC 1313 (4.1 Mpc) [108], M83 (4.5 Mpc) [109], NGC 5068 (5-7 Mpc) [110], NGC 6744 (7-11 Mpc) [111]. Most interesting, perhaps, has been their HST study of M101, a large spiral located at a (relatively speaking) modest 6.7 Mpc distance [112,113], with followup spectroscopy with the Gemini 8-m [114].…”

A Very Large Telescope imaging and spectroscopic survey of the Wolf-Rayet population in NGC 7793★

“…The survey consists of 10 nearby star‐forming galaxies, and one dwarf irregular galaxy, which were largely chosen based on criteria such as distance, star formation rate (SFR) and orientation. To date, five galaxies in our sample have been completed (Schild et al 2003; Hadfield et al 2005; Hadfield & Crowther 2007; Crowther & Bibby 2009 & this work), whilst three are underway and three are in the preliminary stages.…”

A very young component in the pre-eminent starburst region of the Small Magellanic Cloud

“…This radiant flux is also reminiscent of those of giant H ii regions in distant metal-poor galaxies, such as regions A1 and A2 in IC 4662 lying 2.44 Mpc away (Heydari-Malayeri et al 1990;Crowther & Bibby 2009, and references therein). Therefore, N66 offers a valuable template for studying these kinds of distant galaxies with high resolution.…”